The attenuation and damping of vibration and noise created by the operation of heavy machinery, such as bus engines, large electrical motors, compressors, and similar rotating machinery, are problems needing a long lasting solution. This is especially true in the commercial transportation industry because of the large amounts of money spent each year on the maintenance of buses to replace the relatively short lived engine mounts which are currently used to suppress transmission of vibration and noise.
The conventional method of damping vibration and reducing noise created by the operation of an engine is with a T-shaped rubber mount called a motor mount, and which is positioned between the engine and the vehicle frame. A metal cylindrical sleeve runs vertically the height of the motor mount to provide structural rigidity to the mount. A metal bolt passes through the metal sleeve for securing the mount to the frame.
A number of problems have become apparent with the use of a conventional rubber motor mount which makes its use less desirable. Due to the many moving parts associated with an operating engine, a large amount of vibration is created which is transmitted through the mount to the frame which, in turn, is felt by the passengers in the vehicle. The rubber outside portion of the mount serves to dampen some of the vibration, but because of the metal sleeve incorporated in the mount, a substantial amount of the vibration is transmitted through the sleeve. This defeats the purpose of the mount, which, of course, is to dampen the vibration.
A second problem associated with the use of a conventional mount is that because the sleeve is made of metal, there is a metal-to-metal interface between the mount and either the frame or the engine which produces an excessive amount of noise due to the vibration of the engine while it is operating. This is an especially important problem for the transportation industry to eliminate because of their desire to provide a quiet and comfortable ride for passengers.
Another noise problem is created by the conventional mount design because the bolt, which passes through the metal sleeve and secures the mount to the frame, has a tendency to stretch over a period of time due to the vibration of the running engine and therefore causes the bolt to be loose and rattle in the sleeve. Because the sleeve is metal, it is being compressed and it is unable to maintain a snug relationship between the bolt and the sleeve.
A third problem is that the conventional engine mount has a relatively short service life. Because of the shear and torquing forces applied by the motor to the motor mount, the rubber has a tendency to collapse in a relatively short time. Rubber also has a tendency to deteriorate when it comes in contact with gasoline, oil, grease, road salt, or other chemicals and solvents present in an engine environment. As a result of this relatively short service life, a substantial amount of money is spent in replacing the mounts. Not only are maintenance costs high, but there is also a substantial amount of downtime for the vehicle.
Still another problem associated with the conventional motor mount is an identification problem. In a typical bus configuration there can be as many as 11 mounts used in connection with securing the engine and the transmission to the frame, and the mounts to be used are not all the same size. Because the mounts are made of rubber it is difficult to place a permanent identifying mark on it. The usual way to identify which mount is to be used in a particular place is by a color coding scheme. The mounts are painted a particular color to indicate where they are to be used; however, rubber is not an ideal surface for painting and many times the paint does not adhere to the rubber which leads to improper installation. Accordingly, a need exists for an improved motor mount with vibration damping and noise-reducing characteristics, and which has a long service life, is easily identifiable, and significantly reduces maintenance time and costs.